The present invention relates to high-field permanent magnets. More specifically, it relates to permanent magnet structures that provide internal uniform magnetic fields that can be accessed through non-distorting access ports.
One of the most critical problems confronting designers of high-intensity internal magnetic field sources has been accessing the internal field without distorting it. More specifically, those skilled in the art know that drilling an access port in the shell of a magnetic structure that produces an internal magnetic field can significantly distort the uniformity of that internal field.
The following references show many types of magnetic structures that can be utilized for such purposes:
Leupold, U.S. Pat. No. 4,835,506, issued May 30, 1989, entitled "Hollow Substantially Hemispherical Permanent Magnet High-Field Flux Source;"
Leupold, U.S. Pat. No. 4,837,542, issued Jun. 6, 1989, entitled "Hollow Substantially Hemispherical Permanent Magnet High-Field Flux Source for Producing a Uniform High Field;"
Leupold, U.S. Pat. No. 4,839,059, issued Jun. 13, 1989, entitled "Clad Magic Ring Wigglers;"
Leupold, U.S. Statutory Invention Registration H591, published May 7, 1989, entitled "Method of Manufacturing of a Magic Ring;"
Leupold et al., "Novel High-Field Permanent-Magnet Flux Sources," IEEE Transactions on Magnetics, vol MAG-23, No. 5, pp. 3628-3629, Sept. 1987;
Leupold et al., "A Catalogue of Novel Permanent-Magnet Field Sources," Paper No W3.2, 9th International Workshop on Rare-Earth Magnets and Their Applications, pp 109-123, Aug. 1987, Bad Soden, FRG;
Leupold et al., "Design applications of magnetic mirrors," Journal of Applied Physics, 63(8), Apr. 15, 1988, pp. 3987-3988; Leupold et al., "Applications of yokeless flux confinement," Journal of Applied Physics, 64(10), Nov. 15, 1988, pp. 5994-5996; and
Abele et al., "A general method for flux confinement in permanent-magnet structures," Journal of Applied Physics, 64(10), Nov. 15, 1988, pp. 5988-5990.
Leupold, U.S. Pat. No. 5,103,200, issued Apr. 7, 1992, entitled "High-Field Permanent Magnet Flux Source."
These references show many different permanent-magnet structures. Each structure is comprised of a permanent magnet shell that produces a uniform magnetic field of unusually high intensity in an internal cavity. This internal field is accessed through port holes drilled through the structure's shell at predetermined locations. These port holes in the permanent magnet shell, however, disrupt the uniformity of the shell's magnetization, and thus distort the internal field. Consequently, these structures are unacceptable for high precision applications.
One solution to this distortion problem was recently presented by the present inventor in U.S. Pat. No. 5,216,401, entitled, MAGNETIC FIELD SOURCES HAVING NON-DISTORTING ACCESS PORTS, issued Jun. 1, 1993, and incorporated herein by reference. Generally, this patent discloses a technique for altering a prior art flux source such that it provides distortion-free access to its internal uniform magnetic field. More specifically, the size, shape and composition of the shell of an original structure was altered such that the resultant shell produced an internal field having virtually the same magnitude as the original structure, but with non-magnetized shell material at the location where the access ports were drilled. As a result, this non-magnetized material could be removed from the resultant shell without affecting the uniformity and magnitude of the internal field.
The resultant shell, however, required additional permanent magnet material in regions away from the port holes in order to maintain the magnitude of the resultant internal field to be substantially the same as that of the original structure. If this extra magnetic material was not added, the internal field strength would be compromised. Moreover, the resultant shell required the assembly of a plurality of magnetic components having dissimilar magnetization from each other. As a result, structures disclosed under this technique is expensive and difficult to construct.
A pictorial view of the virtual composition of one such structure is shown in FIG. 1. As shown, resultant structure 30 is virtually formed by adding a uniformly magnetized altering-shell M2 to shell M1 of original structure 10. Note that this is not the actual procedure for constructing structure 30, it is only a mathematic rendition of how original structure 10 is altered to design structure 30. As described above, resultant shell 31 is comprised of a plurality of permanent magnet components having dissimilar magnetization magnitudes, some of which are several times the size and weight as the magnetization components comprising original structure 10.
Consequently, this technique is undesirable for those applications where space is at a premium, and where magnetic materials are scarce. As a result, those skilled in the art strongly desire an easier-to-construct, smaller, less-costly magnetic field source that can provide such distortion-free access to an internal field. The present invention fulfills this need.